This invention relates to equipment for the feed of pulverous material to a concentrate burner of a suspension smelting furnace, which enables the feed of solid finely divided material into the furnace to be distributed evenly in the concentrate burner. According to the invention, a vibrating feeder is located between the raw material conveyor and the actual burner, and the concentrate burner feed pipes are equipped with blades for dividing the material.
In a suspension-smelting furnace, the feed of pulverous material such as concentrate, flux and flue dust takes place via the concentrate burner situated on top of the reaction shaft of the furnace. For the sake of simplicity, the term concentrate will be used hereafter in the text to mean all the pulverous material fed into the furnace via the concentrate burner. It is extremely important for the successful operation of the concentrate burner that the concentrate and the process air are mixed evenly as they are discharged from the burner into the reaction space i.e. the upper section of the reaction shaft of the suspension smelting furnace. If this is not the case, the result is on the one hand an area of under-reacted concentrate where the concentrate is above the targeted process-air/concentrate ratio and, on the other hand, an area of over-reacted concentrate where the concentrate is below the targeted process-air/concentrate ratio, whereby a large amount of magnetite is produced as from the reactions. Magnetite is slow to dissolve and impairs the quality of the slag produced so that it raises the viscosity of said slag, and the high viscosity in turn slows down the separation of matte and slag in the lower furnace.
Poor concentrate distribution also has a clear effect on the temperature profile of the reaction shaft: hot areas are generated in the furnace, where the autogenic lining formed by the concentrate and protecting the reaction shaft, undergoes great thermal stress and the result, in the worst case scenario, may lead to the destruction of the reaction shaft wall. There have also been indications that dust formation is more marked when the burner does not function well due to poor concentrate distribution.
In currently used solutions, the concentrate is brought to the concentrate burner from the concentrate feed silo mainly by redler or scraper conveyor, from where the raw material flow for discharge is taken first to the concentrate burner hopper and from there along the concentrate feed pipes to the actual concentrate burner itself. The equipment is constructed in accordance with the spaces being used, so the conveyor and concentrate pipes may be at a 90xc2x0 angle to each other, whereby in changing the direction of flow in the concentrate burner hopper, the concentrate, which is in a slightly fluidized state, behaves like a liquid, and the flow and especially the distribution of the concentrate in the cross-sectional area of the concentrate pipe is uneven, further weakening the distribution of the concentrate in the burner.
In most cases the concentrate is taken to the concentrate burner using two separate concentrate conveyors. In these cases the concentrate distribution to the burner is dependent on the sychronization of the conveyors. Long-term operation with only one conveyor causes similar problems as above as the concentrate is distributed unevenly in the concentrate feed pipes.
An equipment for the evening out of pulverous material feed to a concentrate burner of a suspension smelting furnace has now been developed to solve the problems described above. The raw material flow discharging from the concentrate conveyor is fed to a short vibrating feeder just before the actual burner, where the frequency of said feeder is adjusted so that the concentrate is slightly packed down in the feeder, and is therefore distributed evenly along the horizontal surface of the feeder. It is preferable to equip the concentrate feed pipes, which feed the raw material from the vibrating feeder to the concentrate burner, with partitions. The essential features of the invention will be made apparent in the attached patent claims.
The vibrating feeder belonging to the concentrate burner feed equipment is located in relation to the actual concentrate burner so that the flow of concentrate coming from the feeder is perpendicular to the vertical axis of the burner, whereby the concentrate flow can be distributed evenly after the feeder in the desired amount. Although changing the direction of the concentrate flow was considered a drawback above, in this case it is not, as the concentrate pipes positioned after the vibrating feeder are equipped with partitions, which divide the concentrate evenly over the whole cross-sectional area of the pipes. The divide is further ensured by making small spreaders in the feeder, which improve the exact dispersion in certain points. The concentrate distribution achieved by the vibrating feeder is preserved by dividing the feed pipes from the vibrating feeder to the concentrate burner with partitions, or blades.
The feed equipment according to the present invention as described above works excellently in the case of a single feeder, evening out the flow of concentrate over both time and place. If, however, the arrangement includes two concentrate conveyors and it is wished to operate them asynchronously, the result is once again an uneven distribution of raw material. This situation can be resolved in two ways, depending on whether asynchronous feeding is a regular or rare occurrence.
If an asynchronous feed is desired or obliged to be used on a fairly regular basis, it is preferable to divide both sides of the concentrate intake area of the concentrate burner itself into four segments so that material enters the four segments of the annular discharge channel evenly distributed.
The realization of the equipment modification detailed above in older burner types, however, requires substantial changes. Therefore, in old concentrate burners and in cases where operation with one feeder occurs rarely, it is easier to stop the process and to furnish the concentrate burner feed pipes and the discharge channel with extra blades on the inside, to divide the feed coming from one side only into four sections. The blades are designed so that they can be used in reverse, regardless of which of the two concentrate feeders is in operation.